Based on 7 years' observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS), we investigate the statistical distribution of electric field Pc5 ULF wave power under different geomagnetic activities and calculate the radial diffusion coefficient due to electric field, DLLE, for outer radiation belt electrons. A simple empirical expression of DLLE[]THEMIS is also derived. Subsequently, we compare DLLE[]THEMIS to previous DLL models and find similar Kp dependence with the DLLE[]CRRES model, which is also based on in situ electric field measurements. The absolute value of DLLE[]THEMIS is constantly higher than DLLE[]CRRES, probably due to the limited orbital coverage of CRRES. The differences between DLLE[]THEMIS and the commonly used DLLM[]normalB‐normalA and DLLE[]Ozeke models are significant, especially in Kp dependence and energy dependence. Possible reasons for these differences and their implications are discussed. The diffusion coefficient provided in this paper, which also has energy dependence, will be an important contributor to quantify the radial diffusion process of radiation belt electrons.

[1] Dispersionless injections are a ubiquitous characteristic of substorms. They are defined as simultaneous enhancements in the fluxes of electrons and ions of different energies, and they are often observed near or inside geosynchronous orbit. We model dispersionless electron injections by considering the interaction of an earthward propagating electromagnetic pulse with the preexisting electron population. Such simulations have been performed previously [Li et al., 1993[Li et al., , 1998]; however, they assumed a constant propagation velocity for the transient fields. Observations have shown that substorm injections and associated magnetic signatures do not propagate at constant velocities, but rather slow down as they approach the inner magnetosphere. Between 4.5 and 6.6 R E the injection propagation speeds reach surprisingly low values, of the order of 24 km/s. Nonetheless, the injections still remain dispersionless . In our simulation we vary the pulse speed with the radial distance from the Earth to match the reported propagation speeds and demonstrate that dispersionless injections are achievable under such low propagation speeds. In particular, we simulate the dispersionless injections of 12 February 1991 measured at two radially displaced spacecraft (CRRES and LANL 1990 -095), when they were both around local midnight.

[1] Ultralow frequency (ULF) waves in the Pc4 and Pc5 bands are ubiquitous in the inner magnetosphere and have significant influence on energetic particle transport. Investigating the source and characteristics of ULF waves also helps us better understand the interaction processes between the solar wind and the magnetosphere. However, owing to the limitation in instrumentation and spatial coverage, the distribution of ULF waves in local time and L shell in the inner magnetosphere has not been completely studied. The recent Time History of Events and Macroscale Interactions During Substorms (THEMIS) mission provides unique opportunities to investigate the spatial distribution of ULF pulsations across different L shells with full local time coverage in the inner magnetosphere during solar minimum, with both electric and magnetic field measurements. Pc4 and Pc5 pulsations in the electric field observations are identified throughout 13 months of measurements, covering 24 h in local time. The pulsations are characterized as either toroidal or poloidal (including compressional) mode, depending on the polarization of the electric field. Subsequently, the pulsations' occurrence rate and wave power distributions in radial distance and local time are recorded. While the distributions of both Pc4 and Pc5 events vary greatly with radial distance and local time, Pc4 events are more frequently observed in the inner region around 5-6 R E and Pc5 events are more frequently observed in the outer region around 7-9 R E , which suggests that the field line resonance is an important source of the ULF waves. In the flank regions, the wave power is dominated by the toroidal mode, likely associated with the KelvinHelmholtz (KH) instability. In the noon sector, the Pc5 ULF wave power is dominated by the poloidal mode, likely associated with the solar wind dynamic pressure disturbance. The KH instability plays an important role, suggested by our observations, during the solar minimum when the solar wind dynamic pressure is relatively weak. We also find that the contributions to the Pc5 ULF wave power from the external sources are larger than the contributions from the internal sources. These statistical results are important in characterizing Pc4 and Pc5 waves and also important for any efforts to model the transport of energetic particles in the magnetosphere.

Abstract. The onset of nonadiabatic proton motion is studied using direct integration of the Lorentz The net A/x is extremely sensitive to initial gyrophase and it is shown that for/Sa > 0.01 differences in gyrophase diverge exponentially with repeated equatorial crossings. Because the equatorial gyrophase determines the/x scattering, this implies that the/x scattering is chaotic so that no gyrophase-averaged invariant exists for the nonadiabatic drift motion. Despite this, the average nonadiabatic drift paths are fairly well defined. The resulting hybrid drift consists of dayside adiabatic and nightside nonadiabatic drift. A single nonadiabatic nightside drift path is associated with a family of adiabatic dayside drift paths. If some of the adiabatic drift paths are open to the magnetopause, all of the particles on the family of hybrid drift trajectories will be subject to loss on a timescale comparable to the drift period. Because the nonadiabatic behavior is due solely to field line curvature, the same behavior will be present with a nonzero convection electric field with the important difference that the lower-energy particles will be on open convection drift paths. The hybrid drift path-induced loss effects are therefore most important for higher-energy particles, > 50 keV, whose adiabatic drift paths are closed in the presence of a convection electric field. The implications of nonadiabatic effects for ring current modeling based on Liouville's theorem apply equally well in the zero and finite electric field cases.